1. Field of the Invention
The present invention is directed to liquid crystal display panels. More particularly, methods and systems relating to differential signaling and timing controls for a liquid crystal display panel are provided.
2. Discussion of the Related Art
Liquid crystal display (LCD) panels are used in a wide range of electronic products, including computers, monitors, flat panel displays, and televisions, among others. LCD displays are matrices of liquid-filled cells that form pixels. LCD panels offer the high resolution, refresh rates, and response times necessary for high-definition viewing of software, graphics, videos, and other media.
LCD panels are typically controlled by display system controllers that are responsible for receiving image data from a graphics card, a video controller, a DVD player, etc., and sending it to an external panel timing controller. Some display system controllers may include additional functionality, such as the SupraHD® 780 processor from Zoran Corporation of Sunnyvale Calif., which integrates a display system control processor with an MPEG-2 decoder, an 8VSB demodulator, NTSC video decoder, HDMI interface, low-voltage differential signaling (LVDS) drivers, memory, and other peripherals to provide a single-chip HDTV controller capable of driving various LCD panels. In such systems, the external panel timing controller may transmit the image data to the LCD panel for display. The external panel timing controller may also generate and send complex timing and control signals to ensure that the image data is displayed at the correct time.
Many LCD panels use some form of differential signaling for interaction between the display system controller, external panel timing controller, and the LCD panel itself. Differential signaling is a form of serial communication performed by sending low-voltage electrical pulses over a pair of electrically-coupled wires. An example of a typical differential signal transmission interface 10 is shown in FIG. 1. A driver 12 sends complementary electrical pulses through the wires 14, 16 connected to a receiver 20. These pulses are signals of opposite polarity: an inverted output and a non-inverted output. For example, the inverted output sends out a high to low transmission, while the non-inverted sends out a low to high transmission. Because the differential signals are equal and opposite, they combine to zero and there is no return signal through any other path, particularly through ground. Prior to reaching the receiver 20, the electric pulse is also conducted through a termination resistor 18, which prevents reflections from occurring at the end of the line. Thus, the receiver 20 can compare the difference in voltage between the electric pulses on wires 14 and 16 and, depending on which one is higher, identify the signal as one of a logical high or low (1 or 0). If the signals are not exactly equal and opposite, to ensure that the pulse does not continue to travel through the system and interfere with subsequent pulses, any remaining voltage may then be conducted through and absorbed by a termination resistor 18, before reaching the driver 12.
Differential signaling offers many benefits in the context of LCD panels. First, the balanced differential lines represented by wires 14, 16 have equal but opposite currents, called odd-mode signals. These odd-mode signals tend to cancel each other out, resulting in low electromagnetic interference. Furthermore, the relatively low voltage reduces the signal swing, allowing for communication speeds of over 5 Gigabits per second (Gbps). Using low voltage signals is possible with differential signaling because any electromagnetic “noise” in the form of inductive radiation from nearby components or electrical fields will affect both lines equally, thereby not affecting the voltage difference between the lines. By contrast, single line transmissions must generate a voltage high enough to overcome this background noise. The low power consumption required for differential signaling allows for the integration of many differential signaling channels on a microchip without generating excessive heat or noise.
Several standards implementing differential signaling are known in the art. Such standards include Low-Voltage Differential Signaling (LVDS), mini-LVDS, Reduced-Swing Differential Signaling (RSDS), and Bussed Low-Voltage Differential Signaling (BLVDS). Standard values for the differential output voltage swing, offset voltage, and output currents for LVDS, RSDS, and mini-LVDS are shown in FIG. 2. These standards may differ from one another as to the expected voltage difference, or “swing”; the amount of voltage applied to a single side; and the number of bits that are sent per clock cycle. For example, LVDS is transmitted at a rate of 7 bits per clock cycle, whereas RSDS and mini-LVDS are transmitted at a rate of 2 bits per clock cycle.
The components in LCD panels may utilize several of these standards. For example, the display system controller may transmit image data and timing signals to the external panel timing controller using an LVDS interface. The external panel timing controller may then send the image data to the panel according to the RSDS or mini-LVDS standards.